btrfs: qgroup: use atomic operations for btrfs_fs_info::qgroup_flags

Currently we define btrfs_fs_info::qgroup_flags as u64, to match the
on-disk qgroup status item's flag.

But for now we have only 4 bits utilized for that flag, and since it's
u64 we have no way to properly use the existing atomic bit operations
(requires an unsigned long pointer).

This results in a lot of non-atomic operations inside qgroup code. Some
maybe fine as other locks are involved, but still it's not a good
practice.

Remove those non-atomic operations by:

- Re-define btrfs_fs_info::qgroup_flags as unsigned long
- Define BTRFS_QGROUP_STATUS_BIT_* and BTRFS_QGROUP_RUNTIME_BIT_*
  Instead of the old value define the bit number.

- Use set_bit()/clear_bit()/test_bit() to replace open-coded bit
  operations

- Add one extra check at qgroup status item read time
  To make sure the on-disk flag is still inside ULONG_MAX.
  Otherwise reject the status item and disable qgroup.

- Get rid of unnecessary spinlock when checking a single bit

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 13 insertions, 8 deletions

diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index cc3b9f7dccaf..b6ccaf848e4b 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -1255,13 +1255,16 @@ static inline __u16 btrfs_qgroup_level(__u64 qgroupid)
 }
 
 /*
- * is subvolume quota turned on?
- */
-#define BTRFS_QGROUP_STATUS_FLAG_ON		(1ULL << 0)
-/*
- * RESCAN is set during the initialization phase
+ * The following BTRFS_QGROUP_STATUS_BIT_* are for * btrfs_qgroup_status_item::flags.
+ *
+ * Is subvolume quota turned on?
  */
-#define BTRFS_QGROUP_STATUS_FLAG_RESCAN		(1ULL << 1)
+#define BTRFS_QGROUP_STATUS_BIT_ON		(0)
+#define BTRFS_QGROUP_STATUS_FLAG_ON		(1UL << BTRFS_QGROUP_STATUS_BIT_ON)
+
+/* RESCAN is set during the initialization phase */
+#define BTRFS_QGROUP_STATUS_BIT_RESCAN		(1)
+#define BTRFS_QGROUP_STATUS_FLAG_RESCAN		(1UL << BTRFS_QGROUP_STATUS_BIT_RESCAN)
 /*
  * Some qgroup entries are known to be out of date,
  * either because the configuration has changed in a way that
@@ -1269,14 +1272,16 @@ static inline __u16 btrfs_qgroup_level(__u64 qgroupid)
  * with a non-qgroup-aware version.
  * Turning qouta off and on again makes it inconsistent, too.
  */
-#define BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT	(1ULL << 2)
+#define BTRFS_QGROUP_STATUS_BIT_INCONSISTENT	(2)
+#define BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT	(1UL << BTRFS_QGROUP_STATUS_BIT_INCONSISTENT)
 
 /*
  * Whether or not this filesystem is using simple quotas.  Not exactly the
  * incompat bit, because we support using simple quotas, disabling it, then
  * going back to full qgroup quotas.
  */
-#define BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE	(1ULL << 3)
+#define BTRFS_QGROUP_STATUS_BIT_SIMPLE_MODE	(3)
+#define BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE	(1UL << BTRFS_QGROUP_STATUS_BIT_SIMPLE_MODE)
 
 #define BTRFS_QGROUP_STATUS_FLAGS_MASK	(BTRFS_QGROUP_STATUS_FLAG_ON |		\
 					 BTRFS_QGROUP_STATUS_FLAG_RESCAN |	\